1. Field of the Invention
The present invention relates to a passive equalizer circuit and in particular to a passive equalizer circuit that is incorporated in a front-end of an integrated receiver circuit.
2. Description of the Related Art
High-speed serial data transmission is employed in many signal interfacing standards (e.g., PCI Express, HDMI, and so on). A high-speed serial data transmission system typically includes a transmitter on a source side for generating an electrical signal (e.g., a voltage/current signal) to represent serial data based on a two-level signaling scheme (e.g., a high level to represent logically “1” data and a low level to represent logically “0” data). The high-speed serial data transmission system also includes a transmission line for delivering the electrical signal from the source side to a destination side and a receiver for receiving the delivered electrical signal and detecting the serial data embedded in the electrical signal. The transmission line can be a cable, a PCB (printed circuit board) trace, or a combination of both. In general, the transmission line behaves similarly to a low-pass filter, which causes more attenuation to a high-frequency component of the electrical signal than to a low-frequency component of the electrical signal. As a result, the electrical signal delivered to the destination side is distorted, and a correct detection of the serial data is sometimes difficult unless a proper equalization is performed in the receiver. Equalization seeks to equalize the overall gain in the entire data transmission path for different frequency components in the electrical signal. Since the transmission line behaves similarly to a low-pass filter, a receiver usually employs a high-pass filter for equalization.
In a recent trend, most of the receiver's functions are integrated in a semiconductor integrated circuit (IC). In particular, a receiver IC usually includes an on-chip equalization circuit. Prior art on-chip equalization circuits usually perform equalization using an amplifier with an inductive load or an RC-degenerated amplifier. Such equalization schemes usually demand considerable power consumption due to the nature of using active circuits. What is needed is a passive equalization scheme for an integrated receiver.